1. Field of The Invention
The present invention relates to a novel polymer mixture which is a polymer reinforced thermoplastic polymer, such as an organic fiber reinforced thermoplastic polymer, to a process for its manufacture, and to use thereof for providing reinforced compositions and articles.
2. Background of The Art
Rigidity is an important characteristic of polymer materials, particularly polymeric construction materials. Frequently cost considerations, among other considerations, cause the development of such materials by incorporation of inorganic reinforcing substances, such as talcum, chalk, mica or glass fibers, into an insufficiently rigid polymer material matrix. The drawback of such a technique is that the impact strength of the reinforced material is generally reduced. At the same time, the addition of reinforcing substances tends to negatively influence other characteristics, for example, flow behavior and weldability. The worsening of such characteristics, moreover, becomes even more distinct as increasing amounts of reinforcing substances are added. It is therefore desirable to employ reinforcing substances having the greatest possible reinforcing effect and to employ them only in low concentrations. For industrial applications, fibrous reinforcing substances, particularly short and long glass fibers, are best suited in this respect. On the other hand, however, incorporation of such fibers requires that special measures be taken to prevent breaking the fibers during incorporation and often results in undesirable fiber markings on the finished surfaces of the workpieces.
In addition to inorganic reinforcing substances, rigid polymers are also employed as reinforcing polymers, i.e., stiffening agents for insufficiently rigid polymer material matrices. The mixture of polymers may be homogeneous or heterogeneous, that is, the mixture may be a single phase or a biphase mixture, and, in particular, the reinforcing polymer may be present in the mixture in the form of fibers. However, organic polymer fibers composed of thermoplastic polymers are not known to have any special reinforcing effect. An exception is stretched polyethylene fibers. Although stretched polyethylene fibers are very strong, their application for this purpose is limited. They cannot be employed, for example, for reinforcing polypropylene or polyamides because of their low melting point. Further, their non-polar character frequently requires that additional measures be taken to improve adhesion to the surrounding polymer matrix.
A reinforcing effect as exhibited, for example, by glass fibers, is likewise demonstrated by non-thermoplastic polyparabenzamides (aramids) when employed as short fibers in, for example, polyamide-66. They have the excellent advantage, compared to glass fiber reinforcements, that the extruded composite materials are isotropic in their strength behavior. The incorporation of prefabricated aramid fibers into thermoplastics in industry is expensive, however, as for glass fibers, in that care must be taken to avoid breakage of the fibers. Thus, uniform dispersion of aramid fibers in, for example, polyamide, is possible only with the use of special phase forming agents which ensure the bonding of the aramid fiber to the polyamide matrix (see synthec, 9403 Goldach, 1 (1989), pages 8-11). In polyamide-66, this process has been employed to increase the elastic modulus by 71% by adding 20 weight percent aramid fibers.
A further example of prior art use of an aramid as a reinforcing fiber is the incorporation of polyparaterephthalamide (PPTA) in polyamide-6 by way of precipitation from a common sulfuric acid solution thereof according to Takayanagi et al, J. Macromol. Sci. Phys., B 17, page 591(1980). During precipitation, PPTA forms microfibers which are dispersed in the polyamide-6 matrix. In this way, the modulus of elasticity of polyamide-6 may be almost doubled by addition of 5 weight percent PPTA fibers. Since PPTA is not meltable, however, it is not possible to produce a PPTA microfiber reinforced polyamide-6, by, for example, a melting-mixing process, so that these interesting substances produced according to the Takayanagi process would be obtainable only at considerable expense on an industrial scale.
Accordingly, it is an object of the present invention to provide a polymer mixture by a simple process for reinforcing a thermoplastic polymer with organic microphases suitable for industrial practice, which microphases preferably have the form of microfibers.
It is a further object of the present invention to reinforce a thermoplastic polymer A by reacting a monomer B in a melt of thermoplastic polymer A to form the most rigid possible linear, branched or cross-linked, high or low molecular weight reaction products.
It is yet another object of the present invention to reinforce a thermoplastic polymer A specifically with aramids as the reinforcing polymer by a melt process so that the technically expensive dispersion of prefabricated aramid fibers in, for example, a polyamide, is no longer necessary.
It is still another object of the present invention to reinforce a thermoplastic polymer A using a lower percentage of reinforcing polymer than used by the prior art while maintaining at least a comparable reinforcing effect so as to keep negative influences on characteristics, for example, weldability of the compound substance, as low as possible.